When functioning properly, a heart maintains its own intrinsic rhythm, and is capable of pumping adequate blood throughout a circulatory system. This intrinsic rhythm is a function of intrinsic signals generated by the sinoatrial node, or SA node, located in the upper right atrium. The SA node periodically depolarizes, which in turn causes the atrial heart tissue to depolarize such that right and left atria contract as the depolarization travels through the atrial heart tissue. The atrial depolarization signal is also received by the atrioventricular node, or AV node, which, in turn, triggers a subsequent ventricular depolarization signal that travels through and depolarizes the ventricular heart tissue causing the right and left ventricles to contract.
Some patients, however, have irregular cardiac rhythms, referred to as cardiac arrhythmias. Cardiac arrhythmias result in diminished blood circulation because of diminished cardiac output. Atrial fibrillation is a common cardiac arrhythmia that reduces the pumping efficiency of the heart. Atrial fibrillation is characterized by rapid, irregular, uncoordinated depolarizations of the atria.
In addition to atrial fibrillation, a condition known as ‘sleep apnea’ can also diminish cardiac output and pose various risks to patients, particularly those who are susceptible to heart failure. Sleep apnea is a sleep disorder that involves the temporary cessation of respiratory airflow during sleep. In various scenarios, sleep apnea may be characterized by one or both of pauses in breathing or periods of shallow breathing during sleep.
Sleep apnea is generally considered a medical syndrome that occurs in various forms. One recognized form of sleep apnea is “central sleep apnea,” which is associated with a failure of the central nervous system to automatically initiate and control respiration. Another recognized form of sleep apnea is “obstructive sleep apnea,” which is associated with an obstruction of the airways due to airway collapse. Yet another recognized form of sleep apnea is a mixed form that may include a central nervous system failure to drive ventilatory effort combined with an obstructive apnea.
Possible effects of sleep apnea include daytime sleepiness, impaired alertness, and various associated cardiovascular diseases, which in turn can significantly impair patient lifestyle and increase morbidity risk. In some cases, obstructive sleep apnea can lead to death, due to lack of oxygen to vital organs of the body. Various approaches have been taken to detect and treat sleep apnea.